A radio communication system is increasingly integrated with the Internet, and there is a growing demand from users for variety and quality of radio communication services. For this reason, new-generation radio communication systems in response to demands for radio multimedia and high-speed transmission are actively developed. In such a trend, a MIMO-OFDM technique which combines multi-antenna input/multi-antenna output (MIMO) and orthogonal frequency division multiplexing (OFDM) increasingly attracts public attention.
In a MIMO system, the transmitting side transmits signals using a plurality of transmitting antennas and the receiving side receives signals using a plurality of receiving antennas. Compared to a conventional single antenna transmission method, the MIMO technique can significantly improve a channel capacity and improve an information transmission rate. In the MIMO system, when the number of used transmitting antennas and receiving antennas is larger, the information transmission rate becomes higher. Antenna resources in the spatial domain can be used almost infinitely compared to resources in the time domain, so that the MIMO technique overcomes the bottleneck in shortage of the resources in conventional techniques, and is one of core techniques of a next-generation radio communication system.
Furthermore, the OFDM technique is currently one of the mainstream techniques for realizing a high-speed radio data transmission. In the principle of the OFDM techniques, high-speed data to be transmitted is transmitted using a plurality of orthogonal subcarriers, and therefore the transmission rate on each subcarrier becomes relatively low. The subcarrier orthogonal multiplexing technique of OFDM can further improve spectrum efficiency of the system compared to a normal frequency multiplexing system. In a system using an OFDM technique, the frequency band of an overall signal is divided into a plurality of very narrow subcarrier frequency bands, and therefore flat fading occurs. Therefore, compared to a single carrier system, the OFDM system can realize a balance more readily.
Furthermore, an adaptive transmission technique makes it possible to effectively improve the information transmission rate on an attenuated channel. An adaptive modulation and coding (AMC) technique is one of important adaptive transmission techniques. Its basic concept includes adaptively changing modulation parameters, coding parameters and transmission power used for transmission based on channel characteristics. System performance is improved by transmitting more information when the channel condition is good and transmitting less information when the channel condition is poor. Therefore, according to the adaptive transmission technique, it is possible to realize a higher information transmission rate, lower bit error rate (BER) and lower transmission power.
Therefore, compared to simply using one technique where the above two techniques of MIMO-OFDM and AMC are combined, higher system performance may be obtained. Hereinafter, a radio communication system applying the two techniques of MIMO-OFDM and AMC will be referred to as a “MIMO-OFDM-AMC system.”